1. Field of the Invention
The present invention relates to an engine control unit to be used in an automobile. In particular, the present invention relates to an engine control unit which is improved in heat radiation performance, thereby making it possible to enhance the reliability thereof and to miniaturize the control unit.
2. Description of the Related Art
In the case of the engine control unit for automobiles, motorcycles and the like where gasoline or light oil is employed as a fuel, there has been conventionally employed an engine control unit provided with an injector for injecting the fuel directly into the cylinder of engine in order to enhance the fuel consumption and output of engine. The injector of this kind is called “in-cylinder direct injection type injector”, “direct injection injector” or “DI (Direct Injection)”. Since the engine employing this in-cylinder direct injection type injector is required to use a fuel which is pressurized at a high pressure, a relatively high output is required for driving and controlling the injector as compared with the fuel-injecting system adopted at present as a mainstream in the gasoline engine wherein the fuel is mixed at first with air to form an air-fuel mixture, which is then injected into the cylinder. Furthermore, in order to cope with the high-speed rotation of engine by improving the drive control of injector, the aforementioned high output is required to be transmitted to the injector within a short period of time.
In the case of the engine control unit where a higher output is demanded as described above, heat is caused to develop from the switching devices (for example, MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), IGBT (Insulated Gate Bipolar Transistor)) and a rectifying device (for example, Diode) employed for constituting an injector drive circuit; from a booster coil constituting a booster circuit; and from an electrolytic capacitor during the drive control of the injector. Therefore, for the purpose of enhancing the heat radiation performance of the engine control unit, there has been adopted a packaged structure which is designed such that it is provided with a heat-dissipating member through which the developed heat is enabled to radiate from a control circuit board equipped with the aforementioned electronic components to a housing base constituting an outer casing.
For example, JP Published Patent Application No. 2004-119533 describes a packaged structure of the engine control unit wherein a heat-dissipating sheet is employed.
According to this conventional packaged structure of the engine control unit, the control circuit board thereof becomes larger in size as the number of electronic components to be mounted on the control circuit board is increased, giving rise to the increase in size of the engine control unit. In recent years, there has been an increasing trend to increase the ratio of living space (indoor space) to the entire vehicle size in order to pursue comfortableness of ride, so that the space available for mounting the engine control unit is increasingly limited. Therefore, the miniaturization of the engine control unit is now becoming an indispensable theme to overcome.
Further, in the case of the engine control unit where a higher output is demanded as described above, a packaged structure which is designed such that the heat developed from electronic components is transmitted to the control circuit board and then radiated from the bottom surface of the control circuit board is accompanied with a problem that, since the control circuit board which is made of a resinous material is low in thermal conductivity, the heat radiation performance thereof would be insufficient even if it is tried to transmit the heat developed from the electronic components to the housing and to radiate the heat from the housing. Additionally, it would be difficult to secure the reliability of the engine control unit when the engine control unit is used in severe automobile operation conditions.